This invention relates to a design for a lightweight holographic sighting device for use on firearms and bows.
There are several types of sights utilized with small arms, such as rifles, shotguns, hand guns, bows, and other similar, hand-held weapons, including sights which incorporate holographic images of various one, two and dimensional reticle patterns.
The Compact Holographic Sight disclosed in U.S. Pat. No. 5,483,362 issued to Tai et al describes the design of a holographic sight that is relatively compact. It is currently sold in the commercial market as the Bushnell(copyright) HOLOsight(copyright). Other HOLOsight(copyright) features are disclosed in U.S. Pat. No. 5,815,936 issued to Sieczka et al. The HOLOsight(copyright) is ideal for larger weapons such as rifles or shotguns and works well with larger caliber handguns. This sight, however, is too long and too heavy for some smaller handguns and some bows.
A number of compact hologram displays have been developed, including the edge illuminated holograms disclosed in U.S. Pat. Nos. 4,643,515 and 5,151,800, both also issued to Upatnieks. These hologram displays have a compact, monolithic structure. They also utilize a diffraction or reflection grating to minimize the effects of the wavelength drift of the laser diode light beam. These edge illuminated, monolithic displays however, have not been incorporated into sights because they are relatively expensive to manufacture.
It is thus desirable to reduce the weight and length of the holographic sight to make it practical as a sighting device for weapons of all types and sizes. It is also desirable to produce a design that can be manufactured at a lower cost.
It is therefore an object of the present invention to provide a holographic sight that is short enough in length and light enough in weight to be conveniently used on relatively small handguns and bows.
It is yet another object of the present invention that the sight can be manufactured at a lower cost.
It is yet another object of the present invention to provide a holographic sight including a windage end elevation adjustment mechanism which is stable and precise, yet simple, lightweight, and economical in design.
It is yet another object of the present invention to provide a collimator for a holographic sight which is simple in design, and economical to manufacture.
It is yet another object of the present invention to provide a battery powered sight which allows for quick and easy replacement of the batteries in the field.
In carrying out the above and other objectives, the lightweight holographic sight of the present invention includes a housing and a base which form a compartment containing a laser diode, an associated power source, and optical elements including a mirror, an off-axis collimator, a holographic reflection grating, and an image hologram of the reticle pattern, wherein the optical elements are arranged within the compartment to direct and fold the laser beam in a substantially generally vertical path.
The invention also preferably includes an elevation and windage adjustment mechanism which rotates the reflection grating about generally horizontal and vertical axes to thereby adjust the projected reticle pattern, and a removable battery compartment including a cam surface which is releasably contacted by a cam lever arm pivotally mounted on the housing or the base to allow for tool-less removal of the compartment for battery replacement.
The sight of the present invention is relatively more compact in its length, due to the above described arrangement of the optical elements. The vertically folded light path significantly shortens the sight, which in turn reduces the length of the metallic base and decreases the weight of the unit.
The diverging beam from the laser is collimated by an off-axis reflective collimator which is lighter than an equivalent collimating lens, and diffracted by a reflection grating. The diffracted light illuminates the reticle image hologram to form the holographic aiming reticle.
The base of the present invention also preferably includes a mounting mechanism that quickly and securely mounts the sight onto any standard Weaver(copyright) style scope rail.
As taught in U.S. Pat. No. 5,483,362, the emission wavelength of a laser diode changes with temperature, and the angle of diffraction is a function of wavelength. By simply illuminating a reticle image hologram with a laser diode, the angular position of the reconstructed image will not be stable. The reticle position will shift with a change in the case temperature of the laser diode. To produce a stable reticle image over a wide temperature range, the illuminating beam is diffracted first by a grating. The wavelength dependency can be removed by matching the dispersions of the grating and the reticle hologram. In the sight described in U.S. Pat. No. 5,483,362, a transmission grating bonded onto a prism is used to produce a dispersion equal to, but with the opposite sign of, the dispersion of the image hologram. In a preferred embodiment of the present invention, a reflection grating is used to compensate for the wavelength dependency of the diffraction by the image hologram. The reflection grating is lighter and more compact than the prism/transmission grating combination described in U.S. Pat. No. 5,483,362.
U.S. Pat. Nos. 5,483,362 and 5,815,936 teach that the angular position of the reconstructed reticle image may be changed for elevation and windage adjustments by rotating the image hologram while keeping the illuminating beam stationary. The adjustment mechanism disclosed in these patents is located behind the hologram, which adds to the overall length of the sight. It is made of aluminum to provide the strength needed to hold the image hologram and its metallic frame in place during recoil.
In the preferred embodiment of the present invention, the angular position of the reticle imaged is changed by rotating the reflection grating. The grating is smaller and lighter than the image hologram and is located inside the housing of the sight. Since the grating is not exposed, it does not have to be protected by its own special frame. This allows the elevation and windage mechanism to be made of a molded composite material, such as plastic, instead of metal, which reduces the production cost. The entire adjustment mechanism is located inside the housing, thereby protecting the mechanism from dirt. Moreover, a sight including this reflection grating adjustment mechanism can be shorter in length, which reduces the overall weight of the sight.
In the preferred embodiment, the batteries are placed inside a battery compartment which is then locked securely in place withing the housing via a cam lever.
A parabolic reflector is the ideal collimator but the aspheric surface is costly to produce. To minimize production costs, one embodiment of the present invention includes an off-axis collimator having two spherical surfaces of different radii. The collimator is preferably made of glass. The light passes through the glass, is reflected off the mirrored back surface of the optical element and through the glass again. The curvatures are chosen such that the spherical aberration is minimized.
As taught in U.S. Pat. No. 5,483,362, the brightness of the reticle image may be controlled by the average output power of a pulse width modulated laser diode. Lowering the duty cycle dims the reticle image. The dynamic range of the brightness control is limited by the narrowest pulse width that can be implemented. The disclosure of U.S. Pat. No. 5,483,362 relating to controlling the brightness of the reticle image with pulse width modulation is incorporated by reference herein.
Most mounts that attach an optical scope onto a Weaver(copyright) style rail on a gun use two bolts to tighten the clamps on either two physically separated mounting bases or an integrated mounting base. Because the present invention is significantly smaller than existing holographic sights in both the length and the weight, the mounting mechanism in the preferred embodiment has a single mounting bolt. The use of a single bolt speeds up the mounting and dismounting of the holographic sight. Moreover, the single bolt mount provides better repeatability than the traditional two-bolt mount which is sensitive to the relative tightening torques applied to the two bolts.
The above objects and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.